In Fig.2, the Boltzmann exponential behavior beyond the peak frequency can be easily recognized and the slope decrease with junction temperature can be predicted as well. The spectrum's full width at half maximum (FWHM) and its temperature dependence are determined by both slopes. However, the sharp spectrum cut-off at the low energy side of the peak frequency as predicted by theory is not observed. The measured spectra show an exponential behavior even on the low energy slope. Analogous results have been reported in literature and have been attributed to thermal agitation of the diode's crystal lattice. This behavior justifies the construction of a spectrum model using frequency as variable and starting from an exponential behavior on both sides of the spectrum peak. A first modeling attempt containing a combination of two exponential s has been given by: